What is your confusion specifically? As long as your perimeter router has it's default gateway configured you do not need to add any special routes for internet routing. You may need to explain your setup and what exactly is not working.

To you first question, ISP's either buy or lease large blocks of IP addresses and subnet out smaller blocks to customers. Again, for further information you need to ask more detailed questions.

An Internet service provider (ISP, also called Internet access provider, or IAP) Free ISPs are Internet Service Providers (ISPs) which provide service free of charge. Many free ISPs display advertisements while the user is connected; like commercial television, in a sense they are selling the users' attention to the advertiser. Other free ISPs, often called freenets, are run on a nonprofit basis, usually with volunteer staff. The IP details can be seen through the site I hope this would solve your problem... Thank you...